Accretion definition, an increase by natural growth or by gradual external addition; growth in size or extent. See more.
Alveoli are tiny sacs within our lungs that allow oxygen and carbon dioxide to move between the lungs and bloodstream. Learn more about how they function and quiz your knowledge at the end.
This is where gas exchange takes place in the lungs. Alveoli are tiny balloon-like sacs, in the lungs, where gas exchange takes place and they serve as the barrier between the external environment (the air) and the internal environment (the blood).